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Erbium is a chemical element with the symbol Er and atomic number 68. It is a silvery-white lanthanide metal and part of the rare earths. In nature it occurs only in trace amounts and is typically recovered as a byproduct of processing other rare earth minerals.

Occurrence and naming: Erbium is found in minerals such as gadolinite and xenotime, and it is associated with the mineral-rich region around Ytterby, Sweden. The element was identified in the 19th century, and its name derives from Ytterby, the place linked to the early discovery of several rare earth elements.

Chemistry and properties: As a member of the lanthanide series, erbium typically exhibits the +3 oxidation state, forming Er3+ ions in solution. The metal is relatively soft and tarnishes in air. Its chemistry is dominated by compounds in which Er3+ is coordinated by oxygen and fluorine ligands, among others. Natural erbium contains several stable isotopes and is combined with other rare earths in mineral deposits.

Applications: The most significant modern use of erbium is in optical communications, where erbium-doped fiber amplifiers enhance signal transmission around a 1550-nanometer wavelength. Erbium is also employed in solid-state lasers and specialty glass phosphors. In some nuclear reactors, erbium compounds serve as neutron absorbers for reactor control and shielding.

Isotopes and safety: Natural erbium comprises multiple stable isotopes, including 162Er, 164Er, 166Er, 167Er, 168Er, and 170Er. The element has several synthetic radioisotopes with various half-lives. Like other lanthanides, erbium is handled with appropriate care to avoid inhalation of dust and exposure to skin.